This invention relates to an image forming apparatus having a detachable cartridge for housing a roll of photosensitive sheet.
Of particular interest for application of this invention are photosensitive sheets of the type disclosed, for example, in U.S. Pat. No. 4,399,209 (Japanese patent publication Tokkai No. 58-88739) comprised of a flexible base sheet coated with microcapsules encapsulating a colorless dye and a photopolymerizing agent which hardens by exposure to light. When a photosensitive sheet like this is exposed to an image forming beam of light such as reflected light from an original document to be copied, those of the microcapsules exposed to light harden while those not exposed remain soft such that an invisible image, or a pattern, of selectively hardened microcapsules is formed on the sheet. A visible image can be obtained from such an invisible image by superposingly covering the invisible pattern with an image transfer sheet coated with a developer material and pressing them together such that only those of the microcapsules which are not hardened by exposure to light are ruptured, causing the encapsulated colorless dye to flow out. The developer material is so selected as to have a chromogenic effect on the dye encapsulated in the microcapsules. Thus, the dye flowing out of the ruptured microcapsules becomes visible, producing a visible image on the transfer sheet.
In an image formation process of this type, it is important to protect the surface of the photosensitive sheet coated with microcapsules not only against external light but also against external force before it is exposed to the image forming beam of light because an external force may rupture the microcapsules. One method of achieving this is to prepare the photosensitive sheet in the form of a roll and set it inside the housing structure of the image formation apparatus. An additional advantage of preparing the photosensitive sheet in a rolled form is that it can then be directly wound around a cylindrical drum on the surface of which an exposure point is defined by an optical system. In this manner, the photosensitive sheet can be supplied and transported by the rotation of this drum and feeding rollers and the like for transporting cut sheets from a cassette can be dispensed with. In other words, the coated surface of the photosensitive sheet can be protected against frictional force of these rollers. If the sheet is rolled up and set inside the housing structure, furthermore, it can also be safely protected against exposure to external light.
A rolled photosensitive sheet, however, risks the danger of exposure to light before it is set inside the housing structure of the image formation apparatus. Moreover, a roll of photosensitive sheet to be directly set inside the image formation apparatus is not easy to work with. Thus, there have been ideas of providing a detachably attachable cartridge inside an image formation apparatus for supporting such a roll of photosensitive sheet. With a cartridge of a simple type intended only for protectingly containing an unused roll of photosensitive sheet, however, there still remains the disposal problem of the used part of the sheet because the photosensitive sheet of this type, unlike the photoreceptor of an electrophotographic copier, is not intended to be used over and over again and the used part must be discarded. There has been the idea of cutting off the used part after each copying and throwing it away but it is not convenient for the user if the used part must be discarded after each copy of made. There has also been the idea of providing a shredder to shred the used part after each copying but neither is it convenient because the image formation apparatus would be required to have an accordingly larger housing structure to contain such a shredder inside and also because the user would still have to throw away the shredded pieces from time to time.